The team etched a thin brass plate and placed it in a tank of water. Ultrasound blasted from above sends acoustic waves through the water that cause the plate to resonate with the surface below. The resulting sound pressure lifts objects placed in the tank according to size and density (Physical Review Applied, doi.org/s68).

The team sorted small glass beads from larger ones and glass beads from tin. Zheng says the device could be tuned to sort a range of nano-scale objects.

This article appeared in print under the headline “Choose what floats with a sound sieve”